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Full text of "Soft Circuits"

LED Hula Hoop 



Make] Projects 

hhiiilH ho/ 1 !/ tuMaal/ chare r\icf*f\\tat* 



build, hack, tweak, share, discover,- 



LED Hula Hoop 

Written By: Brookelynn Morris 



TOOLS: 



PARTS: 



Needlenose pliers (1) 
PVC pipe cutter (1) 
Razor blade (1) 
Soldering iron (1) 
Sponge (1) 
Wire cutters (1) 



HDPE plastic tubing (about 12') 
The tubing must be translucent so that 
light can be emitted from within, and 
HDPE's natural color is a translucent 
milky white. It must be stiff, yet easy to 
bend in a circle. The diameter is an 
important consideration: 3 A" tubing is 
less expensive but trickier to fit the 
circuit and battery into, while 1 " tubing 
costs more but gives more options for 
batteries and their holders. A common 
package length is 100', enough for 
almost 10 hoops. 

Measuring tape (1) 

Barbed pipe fitting (1) 
to match tubing diameter, from the 
plumbing or garden section of a 
hardware store 

Electrical Tape (1) 

Switch (1) 

Almost any kind will do. so long as it fits 



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LED Hula Hoop 

into the hoop. 



Lithium CMOS battery (1) 

Resistor (1) 

LED (21) 

Wired) 

Wired) 

like an unbent coat hanger 

Epoxy (1) 

or hot glue; optional 



SUMMARY 

LED hula hoops are so beautiful to watch, and creating a custom hoop is a satisfying 
challenge. Twenty-one LEDs are used in this hoop; 6 are flashing LEDs that cycle through 
the colors of the rainbow. Each light is combined with a resistor and then wired together in a 
classic and simple parallel circuit. 

Be sure to research each part and its specs when creating the circuit design. Each LED for 
this project was chosen for its similar voltage drop, making things simpler by requiring only 
one value of resistor. 

The battery for this project can be a laptop battery like the one used here, or a few AAA 
batteries taped into series. Either way, the tube can be taken apart for the battery to be 
easily changed. Experimentation and thoughtful research will make this project successful. 



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LED Hula Hoop 








Step 1 — Create the 


"rails" 


for the circuit. 




• Determine the circumference of 
your hoop. This example is 126", or 
10 1/2', for a 40" diameter, same 
size as a pro hoop (Wham-O's 
hoops are 30"-36"). Cut 2 lengths 
of the insulated wire at least that 
length plus 1' tails to help thread 
the circuit into the hoop. Mark 1 
length of wire where each LED will 
be placed. The 21 LEDs in this 
hoop were spaced every 6". 

• Mark the second wire with the 
same intervals, but offset 2" from 
those on the first wire. After all the 
marks are made on both wires, use 
a razor blade to strip about 1/2" of 
insulation at each mark. The 
"railroad ties" set into the "rails" will 
be diagonal. 

• This technique has advantages. 
When the wires are inserted into 
the tube, and the rails are pressed 
close together, each contact has 
insulated wire against it, instead of 
another contact. If spaced right, the 
rails are unable to short-circuit 
against each other. (As insurance, 
cover everything with electrical 
tape to prevent catastrophic 
shorts.) 



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LED Hula Hoop 



Step 2 — Solder the components. 




• With the rails complete, begin the ties. Prepare each resistor by cutting the last 1/3 off one 
of its lead wires (it doesn't matter which). With needlenose pliers, curl the cut end of the 
lead onto itself, creating a small loop. 

• Prepare each LED by bending the long lead — the anode (positive) — at a right angle to 
the base of the light. Leave the short lead — the cathode (negative) — straight. Cut the 
last off the end of the anode and slip it into the curled end of the resistor. 

• Take the pliers and curl the LED anode around the resistor, locking them together. This 
makes soldering easier. Now solder the place where the 2 are joined. Repeat this step until 
each resistor has been joined to each LED. 

• Wiring of the switch depends on the switch itself. Mine has 3 leads, but only 2 are needed 
to make the circuit. A 3-lead switch should be tested to see which 2 leads will make an 
open/closed circuit. Now add a few inches of wire to the chosen leads to make the switch 
accessible from inside the hoop. 



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LED Hula Hoop 



Step 3 — Assemble the lights. 






• The 2 wire rails run parallel, one positive and the other negative. Wire all the components 
to the rails by twisting the leads around the sections of stripped wire. Connect the LED 
cathodes to the negative rail and the resistors to the positive rail, placing your colored 
LEDs in any pattern desired. 

• Wire each one, and then, before soldering, press the rail wires against the battery's 
positive and negative terminals to check that all is in working order. If the LEDs do not 
light, check for loose twists and proper polarity. When each LED lights properly, smile. 

• Carefully solder each component to the rails. Wrap with electrical tape any exposed areas 
that could possibly short out. Now mark each end of each wire as positive or negative, for 
later reference. This step is very important. 



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LED Hula Hoop 



Step 4 — Create and thread the hoop. 




• Cut the tubing to 10 1/2'. If it's too tightly coiled, gently bend it, and if necessary, apply 
heat from hot water or a blow dryer to soften it so that it can be plied into a circle. Very 
slowly, thread the circuit into the tube. When I made this hoop, even gentle threading made 
one of the weaker components break, requiring a repair with electrical tape. Go slowly, and 
use the stiff wire to fish out the ends if there is a snag. 

• Choose one end of the tube for the switch and battery. The switch will be set at the outside 
edge of the tube. Determine where to cut the hole, leaving room for the battery, wires, and 
barbed pipe fitting to be stuffed into this end of the hoop. Using a razor blade, cut a small 
hole to set the switch in. Start small, carving out little bits at a time to make a tight fit. 
Press the switch into the hole, running its wires out the open end of the tube. Secure the 
switch with epoxy or hot glue. On the opposite end of the tube from the switch, thread the 
rails through the barbed fitting, and press the fitting into the tube. 



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LED Hula Hoop 



Step 5 — Connect the battery and close. 





• Wire the battery into the circuit. Solder the positive battery lead to one of the switch leads, 
and the negative battery lead to the negative rail that's threaded through the fitting at the 
other end of the tube. Solder the remaining switch lead to the positive rail to complete the 
circuit. Before enclosing the battery and wires, test the switch several times. 

• Push the battery and wires into the hoop. The fit is tight! Press the open end onto the 
barbed fitting to seal the hoop. The tube can be reopened to change the battery by gripping 
and pulling the ends apart. Now flip the switch and blaze up that hoop! 



This project first appeared in CRAFT Volume 06 , page 54. 



This document was last generated on 201 2-1 0-31 04:57:25 PM. 



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